Electron beam clearing and resetting circuits



1960 A. SOMLYODY 2,948,829

I ELECTRON BEAM CLEARING AND RESETTING CIRCUITS Filed May 15, 1958 n 2' n 9 N INVENTOR.

APP/JD SGML YOD Y Ma. fl w A TTORNE Y ELECTRON BEAM CLEARING AND RESE'ITING CIRCUITS Arpad 'S omlyody, Raritan, N.J., assignor to Burroughs Corporation, Detroit, Micln, a corporation of Michigan Filed May 15, 1958, Ser. No. 735,529

15 Claims. (Cl.315-8.5)

- This invention relates generally to multi-position electron beam switching tubes and to circuits for clearing an electron 'beam from a position in the tube and resetting the beam in a selected zero position.

One type of mu-lti-position electron beam switching.

tube, to which the principles of the invention apply, is described in US. Patent No. 2,721,955 to Fan et al. This type of tube includes a central cathode which is surrounded by a plurality of groups of electrodes, each group representing a position at which an electron beam may form and including a target electrode for receiving an electron beam and developing an output signal therefrom, and a spade electrode adapted to 'form and hold an electron beam on its associated target electrode. Each group of electrodes may also include a switching electrode for switching an electron beam fron one group of electrodes to the next under the influence of crossed electric and magnetic fields.

Generally, in the operation of a tube of this type, with all of the tube electrodes carrying their normal positive supply voltages, electrons emitted by the cathode are retained in the vicinity of the cathode, and an electron beam does not form and flow to any of the tube positions. When a spade or switching electrode has its electrical potential suitably reduced, the electric field pattern is altered and an electron beam forms on a target electrode associated with said spade or switching electrode. Ordinarily, the electron beam thus formed may be moved from one position to the next by means of suitable electrical pulses applied to the switching electrodes.

In some applications of these tubes, for example in decade counters or the like, it is desirable to be able to allow the tube to execute a predetermined counting operation, that is, to move an electron beam from position to position until the beam reaches a predetermined position and then to clear the beam and reset it at a selected zero position. Circuits are known for clearing and resetting electron beams in tubes of the type described above. However, such circuits are not completely satisfactory for high speed operation, and, particularly, for clearing an electron beam from the position adjacent to and leading the zero position and then resetting the beam at the Zero position. When this operation is attempted at high speeds, it is found that the beam tends to switch from the zero or desired reset position ahead to the adjacent leading position where it reforms instead.

Accordingly, the principles and objects of the present invention are directed toward-the provision of improved high speedcircuits for clearing and, resetting an electron beam in a multi-position electron beam switching tube. Briefly, the principles of the invention are described as they relate to a multi-position electron beam tube of the aforementioned type which includes aplurality of positions numbered 0, l n, and which is adapted to switch an electron beam trom'position to position. Means are provided for clearing an electron beam from any position in the tube and resetting the beam at the designated position. 'Ihis"op eration is'accomplished by suitably reducing the potential of the spade electrodes from the normal positive operating potential and then forcibly and rapidly returning all but the 0 spade at the 0 position to the positive operating potential. The delay in return of the 0 spade to operating potential is achieved by a suitable time delaynetwork coupled thereto. Thus, the 0 spade carries a lower potential than the other spades for a short period of time and an electron beamiorms and flows to the 0 position. The foregoing operations on the spade electrodes are achieved at high speed by means of closely spaced negativeand positive electrical pulses properly applied thereto.

According to the invention, precautions are taken toprevent the "1 spade at the 1 position from interfering with the resetting of the electron beam at the 0 position and causing the beam to switch instead to the l position. According to one aspect of the invention, the full effect of the negative-pulse which clears the tube is not applied to the 1 spade so that the 1 spade is thus easily returned to a suitably high positive potential by the positive pulse. Thus, the l spade does not adversely affect the 0 spade. According to another aspect of the invention, the positive pulse is applied directly to the 1" spade, whereas it is applied to the other spades through spade resistors. The result of this operation is that the l spade is raised to a higher potential than the other spades, and, again, the 1 spade does not adversely affect the "0 spade.

The invention is described in greater detail by reference to the drawing wherein:

Fig. l is a perspective view of an electron beam switching tube of a type with which the principles of the invention may be employed;

Fig. 2 is a schematic representation of the tube of Fig. 1 and a circuit in which it may be operated; and

Fig. 3 is a schematic representation of the tube of Fig. 1 and a second circuit in which it may be operated.

The circuits described below are particularly suitable for use with a multi-position electron beam tube of the type shown in US. Patent No. 2,721,955 to Fan et al. This type of tube is shown in Fig. 1 as tube 10 and includes, briefly, an envelope 12 which contains a central longitudinally elongated cathode. 14 and ten groups of electrodes spaced radially equidistantly from the cathode and surrounding the cathode. Each group of electrodes includes a generally U,-shaped elongated spade electrode 16 and a generally L-shaped target electrode '18 positioned so that each target occupies the space between adjacent spade electrodes. Each spade electrode serves to form and hold an electron beam on its corresponding target electrode. A generally rod-like switching electrode 20 is also included in each group of electrodes and is positioned between one edge of each target electrode and the adjacent spade electrode. The switching electrodes are known as switching grids. An open-ended cylindrical permanent magnet 22 is provided surrounding the tube envelope and coaxial therewith. The magnet provides an axial magnetic field which is utilized in conjunction with electric fields within the tube to form and switch an electron beam from the cathode to each of the groups of electrodes. The direction in which the beam switches, that is clockwise or counterclockwise, is always the same and is determined by the orientation of the electric and magnetic fields.

Briefly, in operation of tube 10, electrons emitted by the cathode are retained at the cathode each of the spades, targets and switching grids carries its normal operating electrical potential. When a spade or switching grid experiences a suitable lowering of its potential, an electron beam is formed and directed to the corresponding target electrode. The electron beam may be switched from one target electrodeto the-next by thus suitably Patented Aug. 9, 1960- altering the electrical potentials of a spade or switching grid. Under normal operating conditions, whenever electrode voltages are such that a beam might be supported at several positions, the beam will switch to the most leading position and lock in at this position.

A circuit embodying the invention is shown in Fig. 2 wherein the tube 10 is shown schematically in linear form. To simplify the drawing, only four of the usual ten positions or groups of electrodes are shown. These positions are numbered 0, "1, 2, and 9. In the circuit shown in Fig. 2, the cathode 14 is connected through a cathode resistor 24 to a source of reference potential such as ground. Thecathode is also bypassed by a suitable capacitor 25.

With respect-to'the target or output electrodes 18, each target electrode is coupled through a load resistor 30 to a commontargetbuss 32 which, in turn, is connected to a positive D.C. supply voltage, V,,. An output terminal 34 is provided at each target and is adapted to be connected to a suitable utilization device or circuit.

The switching electrodes 20, which are employed to switch an electron beam from position to position within the tube 10, may be connected in any one of a number of suitable ways to provide the desired switching operation. According to one suitable arrangement, as shown, the switching electrodes are connected in two sets, with alternate electrodes being connected together to form a set. The two sets of'switching electrodes are coupled to a suitable source of switching pulses such as a bistable multivibrator 36. The output pulsesfrom each side of the multivibrator serve to switch the electron beam from one position to the next.

Each spade electrode 16 is connected through a spade load resistor 38 to a common spade buss 40; The spade loadresistance for the spade has approximately the same magnitude as the other spaderesistors, but is embodied in two substantially equal resistors 38' and38". The spade buss 40, in turn, is connected through a common spade load resistor 4'to a positive D.C. supply voltage V,'. A clear and'reset pulse source 44 is also coupledto the spade b'uss 40. The source 44 may comprise a conventional blocking oscillator and provides pulses 46 including a negative portion 48 and a positive portion 50. The positive pulse portion 50 comprises, in effect, an overshoot of thehorizontal reference axis by the rising leg of the negative pulseportion. Pulses of this type are of the form usually obtained. from blocking,

connection from the spade boss 40 through adiode f and a capacitor 58 to ground. The diode 56 is oriented with its cathode connected to the spadebuss and its anode connected to the capacitor 58 and to the junction of resistors 38 and 38". The resistor 38 and capacitor 58 pro vide the desired circuit time constant.

A problem often arises when an electron beam is flowing to the 1 position and it is desired to clear the beam from the 1 position and reset it at the 0 position. The problem results from the fact that the electron beam holds the "1 spade at a lower potential than the other spades and the application of the negative pulse 48 would reduce this potential to an-even lower level. Thus, during the resetting operation, when the 0 spade is supposed to be at a lower potential than all of the otherspades, the "1 spade may be at such a low potential that the tube cannot perform thedesired reset-operation and the beam switches immediately from the 0 position ahead to the "1 position.

According to one aspect of the invention, in order to avoid the problem set forth above, a unidirectional current flow dewlce, for example a diode 60, is connected between the spade buss 40 and the spade loadresistor 38 of 4 the "1 spade. The diode 60 is oriented to present its reverse or high resistance to the negative portion of the pulse 46 and thus prevents the full effect of this portion of the pulse from being applied to the 1" spade but allows it to be applied to the other spades.

Operation of the circuit of Fig. 2 is as follows. Let it be assumed that the tube 1'0-i's counting in normal fashion and an electron beam is being switched from position to position under the influence of pulses applied to the switching electrodes 20 from the multivibrator 36. When it is desired to clear and reset the beam, a clear and reset pulse 46 is applied to the spade buss 40. The negative portion 48 of this pulse lowers the spade buss 40 and the spade electrodes 16 to a sufiiciently low potential so that an electron beam cannot be maintained at any of the positions and the beam is cleared. The capacitor 58, which had been charged positive by the power supply, is also discharged by the negative pulse. The diode 60 blocks the negative pulse from being applied to the "1 spade, and since the negative pulse is substantially prevented from affecting the potential of the 1 spade, subsequent resetting of the beam at the "0 position is not adversely affected by the l spade.

When the negative portion 48 of the pulse 46 is terminated, the positive pulse portion 50 is applied to the spade buss 40. This positive pulse speeds the rise of all of the spade electrodes, and particularly the l spade, to their normal operating voltages. However, the spade at the 0 position is held at a reduced potential by capacitor 58 and rises more slowly than the other spades. The rate of rise in potential of spades "1 to 9 is controlled by the time constant of the spade resistors and the capacity between the spades and the other electrodes. The rate at which the O spade returns to normal operating voltage is determined by the time constant of the combination of resistor 38' and capacitor 53. Since the spade at the 0" position is thus maintained at a lower potential than the other spades for a period of time, an electron beam from the cathode forms on the target at the 0 position.

, A modification of the circuit of the invention is shown in Fig. 3. For simplicity, only positions 0 and l in the tube 10 are shown. The circuit of Fig. 3 may be identical with that of Fig. 2 except that the diode 60 (Fig. 2 is removed and a diode 60' is positioned with its cathode connected directly to the 1 spade and its anode connected to the junction point 64 of a capacitor 66 and resistor 68 coupled in series between the spade buss 40 and the cathode 14.

The circuit of Fig. 3 operates in substantially the same way that the circuit of Fig. 2 operates except that in clearing the tube, the negative pulse portion 48 is applied to all of the spade electrodes including spade 1." However, the potentially. adverse etfect of the 1 spade on the resetting operation is prevented by coupling of the positive pulse portion 50 to the "1 spade directly through the diode 60', rather than through a resistor as at spades 2 to "9". Thus, the 1 spade is rapidly raised to a sufiiciently high positive potential so that it does not interfere with the resetting of a beam at the 0 position. This desirable effect takes place even if the electron beam is at the 1 position when the clearing and resetting operation is initiated.

A typical suitable combination of parameters for practising the invention includes the following which are representative but not required:

V spade supply voltage volts positive.

V target supply voltage 300 volts positive.

Pulse portion 48 volts negative.

Pulse portion 50 140 volts positive.

Spade resistors 38 150,000 ohms.

0 spade resistors 38, 38" 68,000 ohms each.

Target resistors 36,000 ohms.

Capacitor 58 15 micromicrofarads.

The circuits of the invention provide efficient, high comprising an electron beam tube including an electronemitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; means coupled to one of said spade electrodes for slowly changing its potential in a predetermined direction, and means coupled to the adjacent spade electrode for rapidly changing its potential in said direction.

An electron beam clearing and resetting circuit comprising an electron beam tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; means coupled to said spade electrodes for reducing their potential; means coupled to one of said spade electrodes for slowly changing its potential in a positive direction; and means coupled to the spade electrode adjacent to said one spade for rapidly changing its potential in a positive direction.

3. The circuit defined in claim 2 wherein said lastnamed meanscomprises a diode coupled directly to said adjacent spade electrode and oriented to pass positive pulses thereto.

'4. An electron beam clearing and resetting circuit comprising an electron beam tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a time delay circuit coupled to one of said spade electrodes for delaying a change in one direction in the potential thereof; and means coupled to a spade electrode adjacent to said one spade for rapidly changing its potential in said one direction.

5. An electron beam clearing and resetting circuit comprising an electron beam tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a common spade buss to which each of said spade electrodes is coupled; first circuit means connected to said spade buss for changing the potential of the buss and the spade electrodes at a predetermined rate between a positive reference potential and a lower potential; second circuit means coupled to a first selected spade electrode for preventing it from reaching said lower potential; and third circuit means coupled to a second selected spade electrode for raising the potential thereof from said lower potential to said reference potential at a slower rate than the other of said spade electrodes so that, for a time, the potential of said selected spade is lower than the potentials of the other spades and an electron beam forms on the target electrode associated with said second selected spade electrode.

6. An electron beam clearing and resetting circuit comprising an electron beam tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form. and hold an electron beamv on its associated target electrode; a common spade buss to which each of said spade electrodes is coupled; first cir-.

cuit means connected to said spade buss for changing the,

potential of the buss and the spade electrodes at a predetermined rate between a positive reference potential and a lower. potential; circuit means coupled to all, of said spade electrodes for raising the potential thereof from said lower potential; and third circuit means coupled to a selected spade electrode for raising the potential thereof from said lower potential to said reference potential at a slower rate than the other of said spade electrodes, so that, for a time, the potential of said selected spade. is lower than the potentials of the other spades and an electron beam forms on the target electrode associated with said second selected spade electrode. v

7. An electron beam clearing and resetting circuit comprisingan electron beam tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to, said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and holdan electron beam on its associated target electrode; a common spade buss; a spade impedance coupled between each of said spade electrodes and said common spade buss; first circuit first selected spade electrode for preventingit from reaching said lower potential; andthird circuit means coupledto -a second selected spade electrode for raising the potential thereof from said lower potential to said reference potential at a slower rate than the other of said spade electrodes so that, for a time, the potential of said selected spade is lower than the potentials of the other spades and an electron beam forms on the target elec- 8. A circuit defined in. claim 7 wherein said second.

circuit means includes a unidirectional current flow device connected between said first circuit means and said first selected spade electrode.

9. The circuit defined in claim 7 wherein said first and second selected spade electrodes are at adjacent positions in said tube.

10. The circuit defined in claim 7 wherein said second circuit means includes a diode oriented to prevent the application of negative pulses to said first selected spade electrode.

11. A beam clearing and resetting circuit comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a common spade buss; a spade impedance coupled between each of said spade electrodes and said common spade buss; an auxiliary impedance between said spade buss and the load impedance connected to a first selected one of said spade electrodes; first circuit means connected to said spade buss for changing the potential thereof at a certain rate between a positive operating potential and a lower reference potential; second circuit means coupled between said first circuit means and said first selected spade electrode for assisting it in reaching said lower reference potential; third circuit means coupled to a second selected spade electrode for preventing it from reaching said lower reference potential; and fourth circuit means coupled to said first selected spade electrode for raising the potential thereof from said reference potential to said operating potential at a slower rate than the other of said spade electrodes so that momentarily said selected spade is at a lower potential than Z the other spades and an electron beam forms on the target electrode associatedwith said first selected spade electrode.

12; The circuit defined in claim 11 wherein said second circuit means'includes a diode and said third circuit means includes a capacitor coupled between a source of reference potential less positive than said operating and reference potentials and the junction point of the auxiliary impedance and the spade impedance of said selected spade electrode, and a low resistance diode connected across said last-named spade impedance.

13. The circuit defined in claim 11 wherein said third circuit means includes a crystal diode connected between the junction point of the auxiliary impedance and the spade impedance of said selected spade electrode and a source of reference potential lower than said operating potential and said lowerreierence potential.

I 14. A beam clearing and resetting circuit comprising an electron beam switching-tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a common spade buss; means for applying a positive operating potential to said spade buss and to said spades; a spade impedance coupled between each of said spade electrodesand said common spade buss; an auxiliary impedance between said common spade buss and the load impedance connected to a first selected one of said spade electrodes; a source of negative voltage pulses coupled to said spade buss for applying negative pulses to said spade buss and thereby lowering the potential of said buss and said spade elec trodes from said operating potential to a lower reference potential; auxiliary means coupled between said spade buss and a second selected'spade electrode for blocking negative pulses from said source from being applied thereto; and means coupled to said first selected spade electrode for raising its potential from the lower reference potential to said operating potential at a slower rate than the other of said spade electrodes when a negative pulse is not present at said spade buss so that said selected spade electrode is, momentarily at least, at a lower potential than the other ofsaid spade electrodes and an electron beam forms on the target electrode associated with said first selected spade electrode.

15. A beam clearing and resetting circuit comprising an electron beam switching tube including an electron emitting cathode and a plurality of groups of electrodes arrayed in electron beam receiving relation with respect to said cathode, each of said groups of electrodes including an electron beam target electrode and a spade electrode adapted to form and hold an electron beam on its associated target electrode; a common spade buss to which each of said spades is connected; separate sources of high and low reference potentials coupled to said spade buss; means coupled between said spade buss and a first selected one of said spade electrodes for assisting in lowering its potential from said high reference potential to said low reference potential; means coupled to a second selected spade electrode for preventing the application thereto of said low reference potential; and time delay means coupled to said first selected one of said spades for raising said first selected spade from said low reference potential to said high reference potential at a slower rate than the other of said spade electrodes are raised so that said first selected spade has, at least momentarily, a lower potential than the other spades and an electron beam forms on the target electrode associated with said first selected spade electrode.

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